Even the best suits need altering. Pants need to be shortened, jackets need to be brought in, sleeves need to be narrowed (yes, you can ask your tailor to slim down your sleeves), and buttons need to be realigned with buttonholes (most guys’ shoulders aren’t entirely even, meaning your jacket often sits a bit askew). You should always buy your correct size, but you then need to have a tailor customize it to your body. It’s the difference between being appropriately dressed and being stylishly dressed.